Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -2503,6 +2503,9 @@
   bool setFPMath(StringRef Name) override;
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    // On MCU we support only C calling convention.
+    if (getTriple().isOSIAMCU())
+      return CC == CC_C ? CCCR_OK : CCCR_Warning;
     // We accept all non-ARM calling conventions
     return (CC == CC_X86ThisCall ||
             CC == CC_X86FastCall ||
Index: test/Sema/callingconv-iamcu.c
===================================================================
--- test/Sema/callingconv-iamcu.c
+++ test/Sema/callingconv-iamcu.c
@@ -0,0 +1,53 @@
+// RUN: %clang_cc1 %s -fsyntax-only -triple i686-intel-elfiamcu -verify
+
+void __attribute__((fastcall)) foo(float *a) { // expected-warning {{calling convention 'fastcall' ignored for this target}}
+}
+
+void __attribute__((stdcall)) bar(float *a) { // expected-warning {{calling convention 'stdcall' ignored for this target}}
+}
+
+void __attribute__((fastcall(1))) baz(float *a) { // expected-error {{'fastcall' attribute takes no arguments}}
+}
+
+void __attribute__((fastcall)) test2(int a, ...) { // expected-warning {{calling convention 'fastcall' ignored for this target}}
+}
+void __attribute__((stdcall)) test3(int a, ...) { // expected-warning {{calling convention 'stdcall' ignored for this target}}
+}
+void __attribute__((thiscall)) test4(int a, ...) { // expected-warning {{calling convention 'thiscall' ignored for this target}}
+}
+
+void __attribute__((cdecl)) ctest0() {}
+
+void __attribute__((cdecl(1))) ctest1(float x) {} // expected-error {{'cdecl' attribute takes no arguments}}
+
+void (__attribute__((fastcall)) *pfoo)(float*) = foo; // expected-warning {{calling convention 'fastcall' ignored for this target}}
+
+void (__attribute__((stdcall)) *pbar)(float*) = bar; // expected-warning {{calling convention 'stdcall' ignored for this target}}
+
+void (*pctest0)() = ctest0;
+
+void ctest2() {}
+void (__attribute__((cdecl)) *pctest2)() = ctest2;
+
+typedef void (__attribute__((fastcall)) *Handler) (float *); // expected-warning {{calling convention 'fastcall' ignored for this target}}
+Handler H = foo;
+
+int __attribute__((pcs("aapcs", "aapcs"))) pcs1(void); // expected-error {{'pcs' attribute takes one argument}}
+int __attribute__((pcs())) pcs2(void); // expected-error {{'pcs' attribute takes one argument}}
+int __attribute__((pcs(pcs1))) pcs3(void); // expected-error {{'pcs' attribute requires a string}} \
+                                           // expected-error {{invalid PCS type}}
+int __attribute__((pcs(0))) pcs4(void); // expected-error {{'pcs' attribute requires a string}}
+/* These are ignored because the target is i386 and not ARM */
+int __attribute__((pcs("aapcs"))) pcs5(void); // expected-warning {{calling convention 'pcs' ignored for this target}}
+int __attribute__((pcs("aapcs-vfp"))) pcs6(void); // expected-warning {{calling convention 'pcs' ignored for this target}}
+int __attribute__((pcs("foo"))) pcs7(void); // expected-error {{invalid PCS type}}
+
+void ctest3();
+void __attribute__((cdecl)) ctest3() {}
+
+typedef __attribute__((stdcall)) void (*PROC)(); // expected-warning {{calling convention 'stdcall' ignored for this target}}
+PROC __attribute__((cdecl)) ctest4(const char *x) {}
+
+void __attribute__((intel_ocl_bicc)) inteloclbifunc(float *a) {} // expected-warning {{calling convention 'intel_ocl_bicc' ignored for this target}}
+
+struct type_test {} __attribute__((stdcall)); // expected-warning {{calling convention 'stdcall' ignored for this target}} expected-warning {{'stdcall' attribute only applies to functions and methods}}